In stoker boilers the combustion process is controlled by means of a direct camera-to-monitor chain. A black-and-white video camera, especially developed for the monitoring of combustion processes, is mounted in the wall of the fire box. A special construction video camera for this application is often called a fire-box monitoring camera. The unprocessed video output signal from the video camera is connected to a monitor. Then, based on the video image, the required control procedures of the stoker boiler, such as the control of a hydraulically driven stoker or quantity of combustion air, are effected. The goal of video signal use has been to define from the video image the location of the flame front which is the principal control parameter, as well as to locate possible craters in the fuel bed which cause an uneven air flow.
In soda recovery boilers the combustion process is monitored by means of a video camera but principal information is obtained via the air feed openings.
A disadvantage of the prior art technique is that the image obtained by using the direct video connection is rather undefined due to the random movement of the flames. Also, the generation of smoke disturbs the image. Consequently, the control information obtained from the video image is mostly approximative and does not provide means for an efficient control of the combustion process. In soda recovery boilers the video image gives relatively little information because most of the radiation emitted by the combustion process does not effectively fall within the range of visible light. Monitoring the process via the air feed openings is awkward and leaves obscured areas in the visible field.